Silicon oxynitride (SiON) and alumina (Al2O3) have been used as main materials in DRAM capacitor dielectric of semiconductor devices hitherto developed. However, in the next generation of semiconductors, reduction in size in devices is required to meet high performance, and a material having further high dielectric constant is required as a material of the next generation of capacitor dielectric. At present, tantalum oxide and niobium oxide are noted as a novel material used in capacitor dielectric.
A method for forming a thin film presently used as a semiconductor device includes physical vapor deposition method (PVD method) by sputtering and chemical vapor deposition method (CVD method). However, the next generation or more of semiconductor production requires to form a uniform and thin film on the surface of a complicated three-dimensional structure of a device having reduced size. Accordingly, PVD method which is difficult to form a uniform film on a patterned indented surface is not appropriate. For this reason, a method for forming a thin film by CVD method of sending a raw material as a gas to a reaction chamber and decomposing the same to deposit a film or an atomic layer deposition method (ALD method) of decomposing a raw material adsorbed on a substrate surface to deposit a film is investigated as a method for preparing a thin film with good step coverage.
In the production of a semiconductor device, a material having appropriate vapor pressure and thermal stability and capable of vaporizing in a stable supply amount is selected as a material for forming a thin film by CVD method or ALD method. Furthermore, it is one of necessary requirements that a film having uniform thickness can be formed on the surface of a complicated three-dimensional structure. Furthermore, it is preferred that a material is liquid at the time of supplying.
Use of amide compounds (for example, Patent Document 1 and Non-Patent Document 1) and pentaalkoxides (for example, Non-Patent Document 2) is investigated as a material for forming a niobium oxide thin film and a tantalum oxide thin film by CVD method or ALD method. However, of the amide compounds, Nb(NtPe)(NMe2)3 is solid at room temperature, and Nb(NtBu)(NEt2)3 and Ta(NtBu)(NEt2)3 are liquid at room temperature, but have low vapor pressure. Pentaalkoxides such as Nb(OEt)5 and Ta(OEt)5 are liquid at room temperature, but have low vapor pressure. That is, those compounds have the respective problems on the use as a raw material for forming a thin film by CVD method or ALD method, and it is difficult to say that those compounds are most appropriate materials.
Patent Document 1: JP-A-2006-131606
Non-Patent Document 1: Journal of Chinese Chemical Society, vol. 45, p. 355 (1998)
Non-Patent Document 2: Chemistry of Materials, vol. 12, p. 1914 (2000)